feat: dukung penjualan produk per timbangan

Produk kini punya cara jual `unit` (cacah) atau `weight` (timbangan),
mengikuti kontrak backend di docs/integration-weight-based-products.md.

- tipe SellBy, domain/infrastructure unit baru, dan endpoint /api/v1/units
- dialog input berat saat produk timbangan ditambahkan ke keranjang
- tiap penimbangan jadi baris keranjang sendiri; total baris dihitung
  berat x harga satuan, sedangkan produk cacah tetap digabung
- request ke backend mengirim quantity 1 dan membawa berat
- migrasi DB v3: kolom sell_by, unit_id, unit_name, unit_abbreviation
  di tabel products supaya satuan tetap tampil saat offline
- tampilan keranjang, struk, split bill, void, dan refund memakai berat
- test/weight_based_products_test.dart menutup perilaku di atas (9 test)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/domain/product/entities/product_entity.dart

@@ -21,6 +21,8 @@ class ListProduct with _$ListProduct {
 
 @freezed
 class Product with _$Product {
+  const Product._();
+
   const factory Product({
     required String id,
     required String organizationId,
@@ -39,6 +41,11 @@ class Product with _$Product {
     required String createdAt,
     required String updatedAt,
     required List<ProductVariant> variants,
+    /// `unit` (default) atau `weight`. Lihat [SellBy].
+    @Default(SellBy.unit) String sellBy,
+    @Default('') String unitId,
+    @Default('') String unitName,
+    @Default('') String unitAbbreviation,
   }) = _Product;
 
   factory Product.empty() => const Product(
@@ -60,6 +67,18 @@ class Product with _$Product {
     updatedAt: '',
     variants: [],
   );
+
+  /// Produk yang dijual per timbangan: `quantity` selalu 1, `weight` wajib.
+  bool get isSoldByWeight => SellBy.isWeight(sellBy);
+
+  /// Singkatan satuan untuk ditampilkan — `ons`. Jatuh ke nama panjang bila
+  /// backend hanya mengirim itu.
+  String get unitLabel =>
+      unitAbbreviation.isNotEmpty ? unitAbbreviation : unitName;
+
+  /// Label harga mengikuti satuan: "Harga per ons".
+  String get priceUnitLabel =>
+      isSoldByWeight && unitLabel.isNotEmpty ? 'per $unitLabel' : '';
 }
 
 @freezed

lib/domain/product/entities/product_quantity_entity.dart

@@ -1,14 +1,53 @@
 part of '../product.dart';
 
+/// Satu baris keranjang.
+///
+/// Untuk produk timbangan, **satu penimbangan = satu baris**: dua kali menimbang
+/// Ikan Tude menghasilkan dua baris terpisah dengan [quantity] 1 dan [weight]
+/// masing-masing. Karena itu baris dibedakan lewat [lineId], bukan lewat
+/// kombinasi produk + varian.
 @freezed
 class ProductQuantity with _$ProductQuantity {
+  const ProductQuantity._();
+
   const factory ProductQuantity({
     required Product product,
     ProductVariant? variant,
     required int quantity,
     required String notes,
+    @Default('') String lineId,
+
+    /// Angka timbangan dalam satuan produk. `null` untuk produk cacah.
+    double? weight,
   }) = _ProductQuantity;
 
   factory ProductQuantity.empty() =>
       ProductQuantity(product: Product.empty(), quantity: 0, notes: '');
+
+  bool get isWeighted => weight != null;
+
+  double get unitPrice => product.price + (variant?.priceModifier ?? 0);
+
+  /// Harga baris: `weight × unit_price` untuk timbangan, `quantity × unit_price`
+  /// untuk produk cacah.
+  double get lineTotal =>
+      isWeighted ? unitPrice * weight! : unitPrice * quantity;
+
+  /// `4,2 ons` atau `2` — dipakai di kolom Qty keranjang.
+  String get quantityLabel {
+    if (!isWeighted) return quantity.toString();
+    final label = product.unitLabel;
+    final value = weight!.weightFormat;
+    return label.isEmpty ? value : '$value $label';
+  }
+}
+
+extension ProductQuantityListExt on List<ProductQuantity> {
+  /// Total keranjang: baris berbobot pakai `weight × harga`, baris cacah pakai
+  /// `quantity × harga`.
+  double get cartTotal => fold<double>(0, (sum, item) => sum + item.lineTotal);
+
+  /// Baris berbobot dihitung satu — satu penimbangan, satu barang.
+  int get cartItemCount =>
+      fold<int>(0, (sum, item) => sum + (item.isWeighted ? 1 : item.quantity));
 }

lib/domain/product/product.dart

@@ -3,6 +3,8 @@ import 'package:flutter/foundation.dart';
 import 'package:freezed_annotation/freezed_annotation.dart';
 
 import '../../common/api/api_failure.dart';
+import '../../common/extension/extension.dart';
+import '../../common/types/sell_by.dart';
 
 part 'product.freezed.dart';
 

lib/domain/product/product.freezed.dart

@@ -286,6 +286,12 @@ mixin _$Product {
   String get updatedAt => throw _privateConstructorUsedError;
   List<ProductVariant> get variants => throw _privateConstructorUsedError;
 
+  /// `unit` (default) atau `weight`. Lihat [SellBy].
+  String get sellBy => throw _privateConstructorUsedError;
+  String get unitId => throw _privateConstructorUsedError;
+  String get unitName => throw _privateConstructorUsedError;
+  String get unitAbbreviation => throw _privateConstructorUsedError;
+
   /// Create a copy of Product
   /// with the given fields replaced by the non-null parameter values.
   @JsonKey(includeFromJson: false, includeToJson: false)
@@ -315,6 +321,10 @@ abstract class $ProductCopyWith<$Res> {
     String createdAt,
     String updatedAt,
     List<ProductVariant> variants,
+    String sellBy,
+    String unitId,
+    String unitName,
+    String unitAbbreviation,
   });
 }
 
@@ -350,6 +360,10 @@ class _$ProductCopyWithImpl<$Res, $Val extends Product>
     Object? createdAt = null,
     Object? updatedAt = null,
     Object? variants = null,
+    Object? sellBy = null,
+    Object? unitId = null,
+    Object? unitName = null,
+    Object? unitAbbreviation = null,
   }) {
     return _then(
       _value.copyWith(
@@ -421,6 +435,22 @@ class _$ProductCopyWithImpl<$Res, $Val extends Product>
                 ? _value.variants
                 : variants // ignore: cast_nullable_to_non_nullable
                       as List<ProductVariant>,
+            sellBy: null == sellBy
+                ? _value.sellBy
+                : sellBy // ignore: cast_nullable_to_non_nullable
+                      as String,
+            unitId: null == unitId
+                ? _value.unitId
+                : unitId // ignore: cast_nullable_to_non_nullable
+                      as String,
+            unitName: null == unitName
+                ? _value.unitName
+                : unitName // ignore: cast_nullable_to_non_nullable
+                      as String,
+            unitAbbreviation: null == unitAbbreviation
+                ? _value.unitAbbreviation
+                : unitAbbreviation // ignore: cast_nullable_to_non_nullable
+                      as String,
           )
           as $Val,
     );
@@ -453,6 +483,10 @@ abstract class _$$ProductImplCopyWith<$Res> implements $ProductCopyWith<$Res> {
     String createdAt,
     String updatedAt,
     List<ProductVariant> variants,
+    String sellBy,
+    String unitId,
+    String unitName,
+    String unitAbbreviation,
   });
 }
 
@@ -487,6 +521,10 @@ class __$$ProductImplCopyWithImpl<$Res>
     Object? createdAt = null,
     Object? updatedAt = null,
     Object? variants = null,
+    Object? sellBy = null,
+    Object? unitId = null,
+    Object? unitName = null,
+    Object? unitAbbreviation = null,
   }) {
     return _then(
       _$ProductImpl(
@@ -558,6 +596,22 @@ class __$$ProductImplCopyWithImpl<$Res>
             ? _value._variants
             : variants // ignore: cast_nullable_to_non_nullable
                   as List<ProductVariant>,
+        sellBy: null == sellBy
+            ? _value.sellBy
+            : sellBy // ignore: cast_nullable_to_non_nullable
+                  as String,
+        unitId: null == unitId
+            ? _value.unitId
+            : unitId // ignore: cast_nullable_to_non_nullable
+                  as String,
+        unitName: null == unitName
+            ? _value.unitName
+            : unitName // ignore: cast_nullable_to_non_nullable
+                  as String,
+        unitAbbreviation: null == unitAbbreviation
+            ? _value.unitAbbreviation
+            : unitAbbreviation // ignore: cast_nullable_to_non_nullable
+                  as String,
       ),
     );
   }
@@ -565,7 +619,7 @@ class __$$ProductImplCopyWithImpl<$Res>
 
 /// @nodoc
 
-class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
+class _$ProductImpl extends _Product with DiagnosticableTreeMixin {
   const _$ProductImpl({
     required this.id,
     required this.organizationId,
@@ -584,8 +638,13 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
     required this.createdAt,
     required this.updatedAt,
     required final List<ProductVariant> variants,
+    this.sellBy = SellBy.unit,
+    this.unitId = '',
+    this.unitName = '',
+    this.unitAbbreviation = '',
   }) : _metadata = metadata,
-       _variants = variants;
+       _variants = variants,
+       super._();
 
   @override
   final String id;
@@ -633,9 +692,23 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
     return EqualUnmodifiableListView(_variants);
   }
 
+  /// `unit` (default) atau `weight`. Lihat [SellBy].
+  @override
+  @JsonKey()
+  final String sellBy;
+  @override
+  @JsonKey()
+  final String unitId;
+  @override
+  @JsonKey()
+  final String unitName;
+  @override
+  @JsonKey()
+  final String unitAbbreviation;
+
   @override
   String toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) {
-    return 'Product(id: $id, organizationId: $organizationId, categoryId: $categoryId, sku: $sku, name: $name, description: $description, price: $price, cost: $cost, businessType: $businessType, imageUrl: $imageUrl, printerType: $printerType, printToChecker: $printToChecker, metadata: $metadata, isActive: $isActive, createdAt: $createdAt, updatedAt: $updatedAt, variants: $variants)';
+    return 'Product(id: $id, organizationId: $organizationId, categoryId: $categoryId, sku: $sku, name: $name, description: $description, price: $price, cost: $cost, businessType: $businessType, imageUrl: $imageUrl, printerType: $printerType, printToChecker: $printToChecker, metadata: $metadata, isActive: $isActive, createdAt: $createdAt, updatedAt: $updatedAt, variants: $variants, sellBy: $sellBy, unitId: $unitId, unitName: $unitName, unitAbbreviation: $unitAbbreviation)';
   }
 
   @override
@@ -659,7 +732,11 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
       ..add(DiagnosticsProperty('isActive', isActive))
       ..add(DiagnosticsProperty('createdAt', createdAt))
       ..add(DiagnosticsProperty('updatedAt', updatedAt))
-      ..add(DiagnosticsProperty('variants', variants));
+      ..add(DiagnosticsProperty('variants', variants))
+      ..add(DiagnosticsProperty('sellBy', sellBy))
+      ..add(DiagnosticsProperty('unitId', unitId))
+      ..add(DiagnosticsProperty('unitName', unitName))
+      ..add(DiagnosticsProperty('unitAbbreviation', unitAbbreviation));
   }
 
   @override
@@ -693,11 +770,17 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
                 other.createdAt == createdAt) &&
             (identical(other.updatedAt, updatedAt) ||
                 other.updatedAt == updatedAt) &&
-            const DeepCollectionEquality().equals(other._variants, _variants));
+            const DeepCollectionEquality().equals(other._variants, _variants) &&
+            (identical(other.sellBy, sellBy) || other.sellBy == sellBy) &&
+            (identical(other.unitId, unitId) || other.unitId == unitId) &&
+            (identical(other.unitName, unitName) ||
+                other.unitName == unitName) &&
+            (identical(other.unitAbbreviation, unitAbbreviation) ||
+                other.unitAbbreviation == unitAbbreviation));
   }
 
   @override
-  int get hashCode => Object.hash(
+  int get hashCode => Object.hashAll([
     runtimeType,
     id,
     organizationId,
@@ -716,7 +799,11 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
     createdAt,
     updatedAt,
     const DeepCollectionEquality().hash(_variants),
-  );
+    sellBy,
+    unitId,
+    unitName,
+    unitAbbreviation,
+  ]);
 
   /// Create a copy of Product
   /// with the given fields replaced by the non-null parameter values.
@@ -727,7 +814,7 @@ class _$ProductImpl with DiagnosticableTreeMixin implements _Product {
       __$$ProductImplCopyWithImpl<_$ProductImpl>(this, _$identity);
 }
 
-abstract class _Product implements Product {
+abstract class _Product extends Product {
   const factory _Product({
     required final String id,
     required final String organizationId,
@@ -746,7 +833,12 @@ abstract class _Product implements Product {
     required final String createdAt,
     required final String updatedAt,
     required final List<ProductVariant> variants,
+    final String sellBy,
+    final String unitId,
+    final String unitName,
+    final String unitAbbreviation,
   }) = _$ProductImpl;
+  const _Product._() : super._();
 
   @override
   String get id;
@@ -783,6 +875,16 @@ abstract class _Product implements Product {
   @override
   List<ProductVariant> get variants;
 
+  /// `unit` (default) atau `weight`. Lihat [SellBy].
+  @override
+  String get sellBy;
+  @override
+  String get unitId;
+  @override
+  String get unitName;
+  @override
+  String get unitAbbreviation;
+
   /// Create a copy of Product
   /// with the given fields replaced by the non-null parameter values.
   @override
@@ -1121,6 +1223,10 @@ mixin _$ProductQuantity {
   ProductVariant? get variant => throw _privateConstructorUsedError;
   int get quantity => throw _privateConstructorUsedError;
   String get notes => throw _privateConstructorUsedError;
+  String get lineId => throw _privateConstructorUsedError;
+
+  /// Angka timbangan dalam satuan produk. `null` untuk produk cacah.
+  double? get weight => throw _privateConstructorUsedError;
 
   /// Create a copy of ProductQuantity
   /// with the given fields replaced by the non-null parameter values.
@@ -1141,6 +1247,8 @@ abstract class $ProductQuantityCopyWith<$Res> {
     ProductVariant? variant,
     int quantity,
     String notes,
+    String lineId,
+    double? weight,
   });
 
   $ProductCopyWith<$Res> get product;
@@ -1166,6 +1274,8 @@ class _$ProductQuantityCopyWithImpl<$Res, $Val extends ProductQuantity>
     Object? variant = freezed,
     Object? quantity = null,
     Object? notes = null,
+    Object? lineId = null,
+    Object? weight = freezed,
   }) {
     return _then(
       _value.copyWith(
@@ -1185,6 +1295,14 @@ class _$ProductQuantityCopyWithImpl<$Res, $Val extends ProductQuantity>
                 ? _value.notes
                 : notes // ignore: cast_nullable_to_non_nullable
                       as String,
+            lineId: null == lineId
+                ? _value.lineId
+                : lineId // ignore: cast_nullable_to_non_nullable
+                      as String,
+            weight: freezed == weight
+                ? _value.weight
+                : weight // ignore: cast_nullable_to_non_nullable
+                      as double?,
           )
           as $Val,
     );
@@ -1229,6 +1347,8 @@ abstract class _$$ProductQuantityImplCopyWith<$Res>
     ProductVariant? variant,
     int quantity,
     String notes,
+    String lineId,
+    double? weight,
   });
 
   @override
@@ -1255,6 +1375,8 @@ class __$$ProductQuantityImplCopyWithImpl<$Res>
     Object? variant = freezed,
     Object? quantity = null,
     Object? notes = null,
+    Object? lineId = null,
+    Object? weight = freezed,
   }) {
     return _then(
       _$ProductQuantityImpl(
@@ -1274,6 +1396,14 @@ class __$$ProductQuantityImplCopyWithImpl<$Res>
             ? _value.notes
             : notes // ignore: cast_nullable_to_non_nullable
                   as String,
+        lineId: null == lineId
+            ? _value.lineId
+            : lineId // ignore: cast_nullable_to_non_nullable
+                  as String,
+        weight: freezed == weight
+            ? _value.weight
+            : weight // ignore: cast_nullable_to_non_nullable
+                  as double?,
       ),
     );
   }
@@ -1281,15 +1411,16 @@ class __$$ProductQuantityImplCopyWithImpl<$Res>
 
 /// @nodoc
 
-class _$ProductQuantityImpl
-    with DiagnosticableTreeMixin
-    implements _ProductQuantity {
+class _$ProductQuantityImpl extends _ProductQuantity
+    with DiagnosticableTreeMixin {
   const _$ProductQuantityImpl({
     required this.product,
     this.variant,
     required this.quantity,
     required this.notes,
-  });
+    this.lineId = '',
+    this.weight,
+  }) : super._();
 
   @override
   final Product product;
@@ -1299,10 +1430,17 @@ class _$ProductQuantityImpl
   final int quantity;
   @override
   final String notes;
+  @override
+  @JsonKey()
+  final String lineId;
+
+  /// Angka timbangan dalam satuan produk. `null` untuk produk cacah.
+  @override
+  final double? weight;
 
   @override
   String toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) {
-    return 'ProductQuantity(product: $product, variant: $variant, quantity: $quantity, notes: $notes)';
+    return 'ProductQuantity(product: $product, variant: $variant, quantity: $quantity, notes: $notes, lineId: $lineId, weight: $weight)';
   }
 
   @override
@@ -1313,7 +1451,9 @@ class _$ProductQuantityImpl
       ..add(DiagnosticsProperty('product', product))
       ..add(DiagnosticsProperty('variant', variant))
       ..add(DiagnosticsProperty('quantity', quantity))
-      ..add(DiagnosticsProperty('notes', notes));
+      ..add(DiagnosticsProperty('notes', notes))
+      ..add(DiagnosticsProperty('lineId', lineId))
+      ..add(DiagnosticsProperty('weight', weight));
   }
 
   @override
@@ -1325,12 +1465,21 @@ class _$ProductQuantityImpl
             (identical(other.variant, variant) || other.variant == variant) &&
             (identical(other.quantity, quantity) ||
                 other.quantity == quantity) &&
-            (identical(other.notes, notes) || other.notes == notes));
+            (identical(other.notes, notes) || other.notes == notes) &&
+            (identical(other.lineId, lineId) || other.lineId == lineId) &&
+            (identical(other.weight, weight) || other.weight == weight));
   }
 
   @override
-  int get hashCode =>
-      Object.hash(runtimeType, product, variant, quantity, notes);
+  int get hashCode => Object.hash(
+    runtimeType,
+    product,
+    variant,
+    quantity,
+    notes,
+    lineId,
+    weight,
+  );
 
   /// Create a copy of ProductQuantity
   /// with the given fields replaced by the non-null parameter values.
@@ -1344,13 +1493,16 @@ class _$ProductQuantityImpl
       );
 }
 
-abstract class _ProductQuantity implements ProductQuantity {
+abstract class _ProductQuantity extends ProductQuantity {
   const factory _ProductQuantity({
     required final Product product,
     final ProductVariant? variant,
     required final int quantity,
     required final String notes,
+    final String lineId,
+    final double? weight,
   }) = _$ProductQuantityImpl;
+  const _ProductQuantity._() : super._();
 
   @override
   Product get product;
@@ -1360,6 +1512,12 @@ abstract class _ProductQuantity implements ProductQuantity {
   int get quantity;
   @override
   String get notes;
+  @override
+  String get lineId;
+
+  /// Angka timbangan dalam satuan produk. `null` untuk produk cacah.
+  @override
+  double? get weight;
 
   /// Create a copy of ProductQuantity
   /// with the given fields replaced by the non-null parameter values.